should i change my solenoid, or the whole starter?

my truck has been starting bad on and off for the last year(basically since i bought it). it used to be everyonce in a while it sounded like a extra heavy drain on battery when trying to start, like the battery had low voltage(but it didnt). since then its gotten worse and worse to the point of now sometimes not starting at all. other times when i try go to start it it starts totally normal(very rare now).

tuesday it wouldnt start at all, i heard the starter engage on the fly wheel once, then after that wouldnt do anything. left it for a couple hours, came back, and started just fine. now today when i wasnt at home it did the same thing. like the starter was totally disabled. tryed boosting, no change. pulled out my hitch and tapped the starter, it engaged but wouldnt turn over. pounded the starter with the hitch, started right up. my next stop was to Canadian tire to pick up a starter, i lucked out, it was on sale($114 for starter, $10 back when i bring in my old one, good price?) champion starter with a 3 year warrenty.

My question is.. should i just go ahead and change the hole starter, or look for just the solenoid at another part store, i would guess saving myself $40-$50. i am on the right track right? it is my starter solenoid?

Ditto on taking it to the parts store.. and you might want to consider having it rebuilt.. I know that it is just cheaper for me to buy a rebuilt one from the parts store for my TBI.. It is $42 US for a rebuilt starter here and the cheapest place i found that rebuilds starters in my area charges $55.. So no brainer but i know up in canada prices can be often skewed a bit from ours.

A common overlooked problem that will give you a crappy battery charge and rob voltage when trying to start your vehicle is corroded battery wires. The blue clumpy corrosion can even creep inside the insulation of the wire if its been there long enough and will be very parasitic when trying to start.